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<head>
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    <title>Document</title>
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</head>
<body>
<div class="dropdown">
    <button class="btn btn-default" data-toggle="dropdown">选择课程 <span class="caret"></span></button>
    <ul class="dropdown-menu">
        <li>a</li>
        <li>a</li>
        <li>a</li>
    </ul>
</div>
<br>
<div class="dropdown">
    <button class="btn btn-default" data-toggle="dropdown">选择课程 <span class="caret"></span></button>
    <ul class="dropdown-menu">
        <li class="dropdown-header">下拉菜单标题1</li>
        <li>a</li>
        <li>a</li>
        <li class="dropdown-header">下拉菜单标题2</li>
        <li class="divider">divider</li>
        <li class="disabled">disabled</li>
        <li>a</li>
        <li><a href="http://www.baidu.com">去百度</a></li>
    </ul>
</div>
</body>
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